1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to pluggable variable optical attenuators.
2. The Background of Related Art
To meet the ever-increasing demands for high bandwidth and more flexibility in modern communication networks, utilizing optical fiber networks capable of transmitting multiplexed channel signals are becoming increasingly popular. DWDM (Dense Wavelength Division Multiplexing) is one of the key technologies for such optical fiber communication networks. DWDM employs multiple wavelengths and channels in a single fiber to transmit in parallel different communication protocols and bit rates. Simultaneously transmitting several channels in a single optical fiber at different wavelengths can expand the transmission capacity of the existing optical transmission systems in multiple folds, and facilitate many useful functions in optical networks.
The channel signals may come from different sources and may have been transmitted over different mediums, resulting in different power levels. Without carefully tuning the power levels of the channel signals that are to be combined or multiplexed, the multiplexed signals in some channels may be distorted. To ensure that all optical devices or systems receive proper levels of optical signals, optical attenuation devices are frequently used in an optical network to adjust the optical signal strength before they reach an optical device.
Variable Optical Attenuator (VOA) is a versatile optical signal power management tool that can help optical network designers and operators to achieve flexibilities in designs and applications. VOA's are widely used in current optical networks from long-haul to metro and even access networks. The adjustment of a VOA can either be manual, thus MVOA, through an adjusting knob or electrical (e.g., via voltage or current signal), thus EVOA. Upon application of a control command, a VOA can attenuate an optical signal arrived at its input optical fiber port so that its output fiber port has lowered the optical power of the same signal by a desired amount. The attenuation is typically measured by decibel or dB and a VOA typically has a continuous tuning capability from “0” dB to “x” dB attenuation based on the application need and the device design specifications. Currently, all VOA's used for optical communications applications are terminated with fiber ports that can be spliced into an optical network directly or with fiber connectors per application requirements.
FIG. 1A shows an MVOA whose attenuation is adjusted manually and fiber ports of both input and output sides are not specially prepared and thus may be spliced by its user. FIG. 1B shows an EVOA where attenuation is adjusted through an electrical signal and its fiber ends are terminated with a pair of fiber connectors.
Pluggable devices are widely available in electronic forms these days. A device that belongs to the pluggable category typically needs to be turned on and function as soon as it is inserted into an electrical connector receptacle or adaptor port. When it is unplugged from such a receptacle, neither the system that hosts the pluggable device nor the pluggable device itself would be damaged. Pluggable devices may be added or removed from a system without interrupting the synchronization between the devices and the system. Therefore, it is not required to have a power reset when replacing or upgrading such devices. Pluggable devices add on a good deal of system application upgrade flexibilities and are becoming more and more popular for electronics.
The advances in opto-electronics also allow people to expand communication transmitters and receivers or the so-called transceivers and transponders into the pluggable domain. Various industry formats for such devices are available: Small Form Pluggable (SFP) is an example. Other examples that allow pluggable applications include XFP, I2C, RS-232, USB, Dual-port RAM, Ethernet, and etc. However, up to today pluggable optical devices has not penetrated into optical passive device, such as the VOA domain.
This invention disclosure intends to introduce various systems to allow VOA devices to be added into the pluggable application categories. The invention is focused on the optical pluggable domain while some devices are also electrically pluggable.